This application requests support for a 2-1/2 day workshop on "The Neuronal Microenvironment" to be cosponsored by the New York Academy of Sciences and the Mount Desert Island Biological Laboratory. The meeting would be held Sept. 4-6, 1985 at the Biological Laboratory and the proceedings of the workshop published by the New York Academy of Sciences. The neuronal microenvironment is a central issue in neurobiology. The physiological activity of neurons in the CNS and hence behavior depends on the composition of the extracellular environment to which they are exposed. The microenvironment is also important as a channel for the transmisson of information within the brain. Recent progress in this area has been made through the use of ion-selective electrodes, the application of concepts and advances in transport physiology, and the development of new techniques for studying the blood-brain barrier. The proposed workshop would consider recent advances in our understanding of the neuronal microenvironment (its composition and functional significance) and of the exchange processes (across the blood-brain barrier and with glial cells) which contribute to the regulation of this environment. Much recent work has established the separate roles of glial cells and of the cerebral endothelium (blood-brain barrier) in influencing and stabilizing the composition of cerebral interstitial fluid. However, there has been little communication between scientists working in these two areas of investigation. By bringing together leading scientists from both groups, with the addition of those concerned with the dynamics and physical chemistry of the interstitial fluid itself, the proposed workshop should be most productive in terms of ideas and future research.